The objective of the following studies is to determine the distribution of estrogen receptor (ER) beta mRNA, its regulation by estrogen and progesterone, and if serotonin neurons express the receptor. Estrogen receptor beta (ERB) mRNA and protein have been localized in the rat brain. In addition, ERB mRNA is regulated by ovarian steroids in the rat brain. Estrogen receptor alpha (ERA) mRNA and protein have also been localized and shown to be regulated by ovarian steroids in the monkey and rat brain. The proposed studies will determine the distribution of ERB mRNA and effects of steroid hormones, using spay, E and E + P treated macaques in brain regions showing ERB mRNA expression in the rat. In addition, expression of ERB mRNA in serotonin neurons will be investigated. Monkey specific ERB probes have been generated and preliminary data has been obtained. The results from these studies will further the understanding of estrogen and progesterone regulation of estrogen receptors in the brain.